C ++ 11从初始化列表到数组参数的隐式转换 [英] C++11 Implicit conversion from initialization list to array parameter

问题描述

在C ++ 11中，是否可以执行以下操作？

In C++11, is it possible to do something similar to the following?

template<typename T, size_t N>
void foo(array<T, N> src) { ... }

...

foo({1, 2, 3})

我当前正在运行GCC 4.8。

I'm currently running GCC 4.8.

推荐答案

是，我设法完成了以下工作（因为您允许类似的东西）：

Yes, I managed to get the following work (since you allow something similar):

template<typename T, size_t N>
void foo(array<T, N> src) { ... }

...

foo('a', 'b');
foo(1, 2, 3);

方法如下：

#include <array>
#include <iostream>
#include <utility>
using namespace std;

template<typename T, unsigned long N>
void foo(array<T,N> src) { 

  for (auto e : src)
    cout << e << endl;
}

template<class T, class... Tail>
auto make_array(T head, Tail... tail) -> std::array<T, 1 + sizeof...(Tail)>
{
     std::array<T, 1 + sizeof...(Tail)> a = {{ head, tail ... }};
     return a;
}

template<class T, class... Tail> 
void foo(T&& head, Tail&&... values) {

    foo(make_array(std::forward<T>(head), std::forward<Tail>(values)...));
}

int main() {

  foo('a', 'b');

  foo(1, 2, 3);
}

我已经用gcc 4.7.2和clang 3.4（trunk 184647）对此进行了测试），它们将按预期工作。

这是在线版本在弯曲的堆栈上。但是，此代码无法在Ideone上编译。由于无法确定在Ideone传递给编译器的选项，因此我放弃了该站点。

I have tested this with gcc 4.7.2 and with clang 3.4 (trunk 184647), they work as expected.
Here is an online version at Stacked-Crooked. However, this code fails to compile at Ideone. Since I was unable to figure out the options passed to the compiler at Ideone, I've given up on that site.

我从 @Pavel Minaev 偷了 make_array 函数>对如何使用以下方法模拟C数组初始化 int arr [] = {e1，e2，e3，…}行为的答案std :: array？问题。其他 make_array 建议导致了我无法修复的编译错误。

I have shamelessly stolen the make_array function from @Pavel Minaev's answer to the How to emulate C array initialization "int arr[] = { e1, e2, e3, … }" behaviour with std::array? question. The other make_array suggestions caused compile errors that I couldn't fix.

此 make_array 函数有局限性，请阅读整篇文章；特别是讨论 std :: array-如果仅知道它的大小在comp.lang.c ++。moderated上被引用。显然，要获得一个合理的 make_array 是很棘手的。 我不建议在此答案中使用思维简单的 make_array 在生产代码中使用。

This make_array function has limitations, please read the entire post; in particular the discussion std::array - if only it knew its size on comp.lang.c++.moderated is referenced. Apparently, getting a reasonable make_array is quite tricky. I wouldn't recommend the simple-minded make_array in this answer to be used in production code.

如果大小是 std :: initializer_list 的模板参数，则不会有任何问题。因此，问题为什么大小不是std :: initializer_list的模板参数？

You wouldn't have any problems if the size was a template argument to std::initializer_list. Hence the question Why is the size not a template argument of std::initializer_list?

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